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Fo rm w o rk ca n be simple an d stra i g h t f o rw a rd whe n
th e de-sign er re c o g n i zes th e fun da m en ta l st ru c t u
ral re q u i re-men ts of each m em ber m aking up th e form ing
system. Each
p a rt of th e form w o rk m ust be within th e allowable limits
for
ben ding, shear, and deflection. Once these requirem ents
are
m et, a stru c t u rally sou nd formin g system can be bu ilt.
By
comb ining what would o therwise be lengthy calculat ions
into a series of charts the an swers can be found in a few
min-
utes. Such charts for vertical forming are given on the opp
o-
site p age. A similar set o f charts for h ori zon tal form s
will be
pu blished in an early issue.
The c ha rts p rovide a q uick re f e rence and are e specially
in-
ten ded for t he sm aller con tra c t o r s. The y will also
prove va l u-
ab le to th e est ima tor who is pre p a ring b ids for form w o
rk, and
they will aid th e con tractor or en gineer in p re p a ring or
ch eck-
ing shop dra w i n g s.
The cha rts for ve rtical form w o rk p rovide informa tion
on
th e follow i n g :
Rate of con crete placemen t
Plywood t hickness
Si ze and spacing of stu ds
Wale size an d spa cing
Fo rm tie spacing an d load on ties
The charts d o no t cover stiffbacks need ed for alignm ent,
nor do th ey provide for bracing neede d for later al stability.
Re-
m em ber that th e ve rtical form s mu st be strong eno ugh to
re-
sist wind or other lateral loads. It is recomm end ed tha t they
be
capa ble of resisting at least 100 po un ds pe r lin eal foot at
th e
top of the form .
Ce rtain com prom ises we re m ade in estab lishing the chart
s
to take care of as ma ny situa tions and o ption s as po
ssible
without making the m com plex an d u nre a s o n a b l e. They a
re in
com pliance with the Am erican Co n c rete Institut e sta nd ard
,
Ch a r t s s im p lify d e -
s ign o f
ve r t ic a l fo r m wo r k
Select or check sheath ing,studs, and wa les
withou t tedious ca lcula tions
BY PAUL H. SOMMERSCHIEF ENGINEERALGERNON BLAIR INCORPORATEM
ONTGOMERY, ALABAMA
HOW TO USE THE DESIGN CHARTSFOR VERTICAL FORMS
Start in the upper left-hand corner. The dottedline shows a s
ample problem which has alreadybeen worked out.
1 . CHOOSE RATE OF POUR. Enter at the t opof the upper left-hand
chart. Go down from t heselected rate of pour (Point A) to the line
repre-senting the expected concrete tem perature
(Point B). Many contractors select 5 0 degrees Ffor cool weather
and possibly 70 degrees forwarm weather.
2 . CHOOSE PLYWOOD THICKNESS. Two choic-es are available in this
chart. Draw a horizontall ine from Point B across to the curve for
the de-sired plywood thickness (Point D). Notice thatthe concrete
pressure can be read at Point C,where this l ine crosses t he
border of the firstchart.
ALTERNATE: You could ass ume a pressureand start from a point at
the edge of the chart,and then later adjust the rate of pour with
tem -
perature to establish the des ired pressure level.3. FIND STUD
SPACING. From Point D draw a
vertical l ine downward to the matching plywoodthickness in the
next char t at Point F. Read atPoint E the m aximum plywood span.
THIS IS AL-SO THE MAXIMUM STUD SPACING. Remem berthe assumption
that plywood is used the strongway with face grain at right angles
to the sup-ports.
4. FIND SPACING OF WALES. From Point Fdraw a horizontal l ine to
the left into the adjoin-ing chart unti l i t intersects t he cur
ve for desiredsize of stud (Point G). With the plywood and stud
sizes selected, draw a vertical l ine downwardfrom Point G to
intersect t he companion curve inthe chart below at Point K. As you
cross over thechart border, read the st ud span at Point H. THISIS
ALSO THE WALE SPACING.
5. FIND SPACING OF FORM TIES. From PointK draw a horizontal l
ine to the right to intersectthe s olid l ine representing the des
ired size ofwales. Mark t he Point M , and draw a vertical l
inedown to the bottom of the chart at Point P. Readthe m aximum
span of the wales here. THIS ISALSO THE MAXIMUM SPACING OF THE
FORMTIES.
6. FIND LOAD ON THE TIES.Where this lastvertical l ine
intersects a dashed line correspond-
ing to the wale s ize selected, mark Point N anddraw a final
horizontal line to Point Q on theright. READ THE TIE LOAD at Point
Q.
7. SAFETY FACTOR FOR TIES. In selecting thestrength of a form
tie, remem ber that ACI 34 7recommends a safety factor of at least
2.0 formost work.
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ACI 347-78. Most of th e d ata for t he cha rts we re ta ken
f rom ACI Special Pu blicat ion No. 4, Fo r m w o rk for Con
-
c re t e .
DESIGN STANDARDS AND STRESSES
Listed below are the working stresses and som e oth er
assum ptions used in pre p a ring the cha rt s.
Plywood sheathing
Plywood is assum ed to be con tinuo us over fou r orm o re sup p
ort s, and it is used the strong waythat is
with face grain pa rallel to the sp an.
Bending stressf= 1930 ps i
Rolling shear vr= 80 psi
Modulus of elasticityE= 1,500,000 psi
These are stresses recom m en ded by th e Am eri c a n
Plywood Associat ion for Pl y f o rm Class I ba sed on sho
rt
t e rm loading.
Lumber or timbers
The wood m emb ers are assumed continuous over two
or m ore spa ns. The allowable stresses are su itable for
usewith No.2 Douglas fir- l a rch su bject to repeate d usage
or
for No. 2 So u t h e rn pin e wh ich will have on ly limite
d
re u s e.
Bending stressf= 1500 psi
Ho ri zon tal shearH= 140 psi
Modulus of elasticityE= 1,700,000 psi
Pressure acting on vertical forms
The lateral p re s s u re of th e c oncrete was b ased on
for-
m u las in ACI 347-78, Section 2.2.2. For the se ch art s,
ma xim um rate of placem ent is l im ited to 10 feet p er
h o u r. Fo rm w o rk with rate s o f placem en t faster t han
10
feet p er hou r should b e an alyzed in greater detail.
SUMMARY
Fo r m w o rk for Con cre t e , AC I s Special Pu blic at ion
No. 4 ,
p rovides m an y design ta bles which redu ce working tim ein th
e pre p a ration of form w o rk sho p dra w i n g s. Howe ve r,
design cha rts like the on e presen ted h ere can take eve n
m o re m ath em atics ou t of t he design wo rk an d re d u c
e
mo st calculations to simple ari t h m e t i c. It is h op ed
tha t
this will help th e craftsm an o r the sm all con tractor to
build forms with some engineering logic an d n ot by em-
p i rical guesses.
Editors note:
Information in this article was condensed from a talk,
Sim-plified Design of Formwork, presented by Paul H. Sommersat a
seminar on quality concrete construction sponsored bythe ACI Kansas
and Missouri Chapters at the ACI conven-tion in Kansas City,
September 27, 1983.
Formwork for Concrete, by M. K. Hurd, referred to by Mr.Sommers,
is also available from Concrete ConstructionPublications. It
contains the complete text of the referencedACI Standard
347-78.
PUBLICATION #C840392
Co py right 1984, The Ab e rdeen Gro u p
All r igh ts re s e rve d
